TFT array substrate and method for producing the same

Abstract

A TFT array substrate has an organic insulating film formed of a photosensitive organic resin material. A common electrode and a lead-out wiring are formed on the organic insulating film, and a pixel electrode is formed above the common electrode with an interlayer insulating film provided between them. The pixel electrode is connected to the lead-out wiring through a contact hole formed in the interlayer insulating film. The lead-out wiring and the common electrode are connected to a drain electrode and a common wiring, respectively, through contact holes formed in the organic insulating film. A metal cap film is provided on each of the lead-out wiring and the common electrode in the contact holes formed in the organic insulating film.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to a thin film transistor (TFT) array substrate and a liquid crystal display device including the same, and more particularly, to a fringe field switching (FFS) mode thin film transistor array substrate in which a pixel electrode and a common electrode are arranged on a planarizing insulating film so as to be opposed to each other through an insulating film, and a liquid crystal display device including the same.[0003]2. Description of the Background Art[0004]In general, a display mode of the liquid crystal display device is broadly classified into a twisted nematic (TN) mode, and a lateral electric field mode represented by in-plane switching (IPS) mode or a fringe field switching (FFS) mode. The liquid crystal display device of the lateral electric field mode is wide in viewing angle and high in contrast.[0005]According to the liquid crystal display device of the IPS mode, display is impl...

AI Technical Summary

Benefits of technology

This patent is about a new method for making a TFT array substrate for liquid crystal displays. The method prevents defects and increases in resistance in certain parts of the substrate. It also reduces the number of steps needed to make the substrate. Overall, the method improves the quality and efficiency of producing TFT array substrates. Additionally, the patent provides a new design for the substrate that prevents alignment issues and other defects.

Problems solved by technology

According to the liquid crystal display device of the IPS mode, display is implemented by applying a lateral electric field to liquid crystal sandwiched between opposed substrates, but since a pixel electrode and a common electrode to apply the lateral electric field are provided in the same layer, liquid crystal molecules positioned just above the pixel electrode cannot be sufficiently driven, so that its transmittance is low in this case.

However, regarding the above TFT array substrate including the thick planarizing insulating film, since a contact hole is deep, a new problem arises.

In a case where the planarizing insulating film is formed of a photosensitive resin or the like, an aspect ratio of the contact hole is high, so that the interlayer insulating film is not likely to be uniformly formed in the contact hole.

In addition, as the interlayer insulating film becomes thin, a covering defect such as a pinhole is likely to be generated in a bottom and a slope part of the contact hole.

When the pinhole is generated in the interlayer insulating film, an etching solution used when the upper transparent conductive film is processed passes through the pinhole and dissolves the lower transparent conductive film, which causes a connection defect and a resistance increase.

However, this is not satisfactory in view of a problem in alignment accuracy in photoengraving process caused when a glass substrate is big, or a case where an etching residue is generated in an isolated part.

However, in order to completely fill the contact hole, a substantial amount of the liquid material needs to be applied to a substrate surface, and as a result, the insulating film is left between the pixel electrode and the opposed electrode, so that it is extremely difficult to reduce only the thickness of the insulating film between the pixel electrode and the opposed electrode.

Furthermore, the liquid material is high in cost.

In addition, the FFS structure including the planarizing insulating film has the problem that a large number of masks are needed in its producing process and production cost becomes high.

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